1. Field of the Invention
The invention concerns a collar for measuring the lateral deformation of a test piece during compression tests, in particular uniaxial or triaxial. It will find a particular application in a polyvalent triaxial test cell for rock sample geomaterials, such as soil, concrete and cimentitious materials or fabricated materials, on the sampling sites, in laboratory test conditions.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Such samples, also called test pieces, cylindrical in shape, may be subjected to different pressure conditions, load, temperature, and drainage conditions, wherein said parameters may be controlled using pressure, temperature, internal or external displacement sensors. The pressure stresses may be directed axially and/or to the lateral face of the sample.
Document FR-2.566.531 divulges a lateral displacement sensor, in the form of a collar, formed by a plurality of parallel rolls, hinged together, and capable of clamping the sample held by a spring-loaded system. Such collar enables measurement of the lateral deformation of the sample while measuring the spacing of both last rolls.
Document FR-2.663.121 divulges a polyvalent triaxial test cell for geomaterials. Such a cell includes a pressure chamber inside which is placed the cylindrical test piece. It includes at least one compression jack capable of exerting uniaxial thrust longitudinally to the test piece.
A lateral pressure, and more particularly radial, is exerted on the test piece while subjecting the lateral face of said cylindrical test piece to the pressure of a fluid. A hydraulic compensation system enables moreover to balance the longitudinal and radial loads.
Also, the sample is immersed in a fluid, such as oil, and is protected from said fluid by means of a sheath in the form of a sleeve formed of an elastic diaphragm. In order to measure the lateral deformation of the sample, a collar of known type, formed of rolls, is placed around the sheath while hugging it.
Nevertheless, such a collar proves little satisfactory, since these rolls have a tendency to impress in the elastic wall of the diaphragm, thereby disturbing their displacement by rolling around the periphery of the sleeve.
Moreover, it has been noticed that the elasticity of the wall of the diaphragm twists the measurement, wherein the collar measures the lateral deformation of the sample, but also the lateral deformation of said diaphragm.
Moreover, the collar known aforementioned, formed of rolls, proves relatively cumbersome and requires a test cell whereof the pressure chamber is sufficiently large, in particular in width, to be installable.